The demand for rechargeable batteries having ever-greater energy density has resulted in substantial research and development activity in rechargeable lithium batteries. The use of lithium in batteries is associated with high energy density, high voltage, long shelf life, but also with safety problems (i.e. fires, reactivity with oxygen and water), since lithium is a highly reactive element. As a result of these safety problems, most of large rechargeable lithium batteries are unsuitable for use by the public. In general, batteries with electrochemistries employing pure lithium metal, lithium carbon or lithium alloy anodes are only available to the public in very small sizes (e.g. coin cell size) or are primary types (e.g. non-rechargeable). However, larger rechargeable batteries can be used for military applications or certain remote power applications where safety concerns are of somewhat lesser importance, or the personnel involved are trained to deal with the higher level of hazard.
This invention pertains to lithium batteries or cells of the type set forth in which the anode or negative electrode includes or consists of a crystalline graphite or lithium metal or lithium alloy and an electrolyte of a salt such as lithium hexaflurophosphate dissolved in an organic solvent consisting of two or more aprotic constituents, one of which may be propylene carbonate as well as a positive electrode such as a lithium metal oxide. Propylene carbonate (PC) based solvents normally cause exfoliation of a graphite negative electrode resulting in the degradation of its electrochemical properties. Propylene carbonate, however, is an excellent solvent for use in lithium ion cells in that it permits cell operation to cross a broad temperature range with graphite based negative electrodes, which provide excellent power characteristics.